Like all JBL products , performance is the last priority, the S100a does one thing good ..that's rock , the treble is not that grainy , making it excellent for rock , its rolled off too not in a bad way , its the 6XX roll off , almost perfect roll off ....which is very odd for a IEM like the S100a

I really enjoy it , very good indeed ..I think it should sound excellent with a nice neutral low OI amp

The mids are a great , they are not distant and recessed like some IEMs .....they don't sound thin or overly thick , almost perfect

There is some missing information in the lower mids as the transition is not that good , the upper bass is a bit bloated and the mid bass is a bit recessed , so it might sound a little confused at times

Not for the Hip-Hop lovers since the Mid-Bass is recessed , not for classical since the treble is rolled off but excellent for Jazz and Rock , the dark tone makes those genres sound sweeeeeet !!!!

The build is excellent , comfort not so much .the remote weighs it down a bit , cable is a flat style cable which is nice , good IEM ....recommended if it ticks the boxes for you , thanks for reading .....have a good one !